1. Field of the Invention
The present invention relates to an apparatus for determining a black point on a display and a method of performing the same.
2. Description of the Related Art
Conventionally, it has been known that CRT displays have a non-linear display characteristic on input value X applied to a display driver vs. relative brightness Yd as shown in FIG. 1. A transit input value X leaving the zero level of the relative brightness is called "Black Point (BP)". As is well known in the art, by representing the minimum level of each of the input value X, the relative brightness Yd with a digital number 0 (zero), and the maximum level thereof with a digital number 255, the display characteristic of the CRT displays can be approximated with the following exponential functions.
When X&lt;BP, then Yd=0.
When X.gtoreq.BP, then EQU Yd={(X-BP)/(255-BP)}.sup..gamma. .times.255
where .gamma. is a predetermined constant specific to the CRT display but is changeable due to, for example, aging of the CRT display.
The black point BP can be changed by a brightness adjusting mechanism provided in the display. The black point also changes due to aging of the display and is seen to be different in level depending on the perception of individuals watching the display. The exact level of the black point BP can make it possible to match the input value with the actual perceived color.
Here a conventional method for determining the black point will be described. As shown in FIG. 2, a reference brightness region A corresponding to X=0 and a comparison brightness regions B corresponding to X&gt;0 are displayed side-by-side on a display. The user increases or decreases the input value for the comparison brightness region B until the comparison brightness region B is first distinguishable from the reference brightness region A. The black point is determined based on the input value at which the distinction between the two regions is first possible.
However, quick determination of the black point may not be achieved if the extent to increase or decrease the input value is not controlled precisely. It has been desired that the determination of the black point be readily feasible for a person who is not accustomed to the above-described method.